A first example of an imaging arrangement for use in an autostereoscopic display device of this type of display is a barrier, for example with slits that are sized and positioned in relation to the underlying pixels of the display. In a two-view design, the viewer is able to perceive a 3D image if his/her head is at a fixed position. The barrier is positioned in front of the display panel and is designed so that light from the odd and even pixel columns is directed towards the left and right eye of the viewer, respectively.
A drawback of this type of two-view display design is that the viewer has to be at a fixed position, and can only move approximately 3 cm to the left or right. In a more preferred embodiment there are not two sub-pixel columns beneath each slit, but several. In this way, the viewer is allowed to move to the left and right and perceives a stereo image in his/her eyes all the time.
The barrier arrangement is simple to produce but is not light efficient. A preferred alternative is therefore to use a lens arrangement as the imaging arrangement. An array of elongated lenses extending parallel to one another overlies the display pixel array and acts as a view forming means. These are known as “lenticular lenses”. Outputs from the display pixels are projected through these lenticular lenses, which function to modify the directions of the outputs.
The lenticular elements are provided as a sheet of elements, each of which comprises an elongate partial-cylindrical (e.g. semi-cylindrical) lens element. The lenticular elements extend generally in the column direction of the display panel, with each lenticular element overlying a respective group of two or more adjacent columns of display sub-pixels.
The display panel for example comprises a two-dimensional liquid crystal display panel having a row and column array of display pixels (wherein a “pixel” typically comprises a set of “sub-pixels”, and a “sub-pixel” is the smallest individually addressable, single-color, picture element). The sub-pixels together act as an image forming means to produce a display.
In an arrangement in which, for example, each lenticule is associated with two columns of display sub-pixels, the display sub-pixels in each column provide a vertical slice of a respective two dimensional sub-image. The lenticular sheet directs these two slices, and corresponding slices from the display pixel columns associated with the other lenticules, to the left and right eyes of a user positioned in front of the sheet, so that the user observes a single stereoscopic image. The sheet of lenticular elements thus provides a light output directing function.
In other arrangements, each lenticule is associated with a group of four or more adjacent display sub-pixels in the row direction. Corresponding columns of display sub-pixels in each group are arranged appropriately to provide a vertical slice from a respective two dimensional sub-image. As a user's head is moved from left to right, a series of successive, different, stereoscopic views are perceived creating, for example, a look-around impression.
Increasing the number of views improves the 3D impression but reduces the image resolution as perceived by the viewer, since all views are displayed at the same time by the native display. A compromise is typically found whereby a number of views (such as 9 or 15) are displayed in so-called viewing cones, and these viewing cones repeat across the field of view. The end result is a display with a large viewing angle, although viewers are not entirely free in choosing their location from which to view the 3D monitor or television: at the boundaries between viewing cones the 3D effect is absent and ghost images appear. This wide viewing angle is a problem in situations where the user of the display would prefer no eavesdropping on all or certain parts of the display content. One typical example is reading of mail and documents during commutes.
It has been proposed to provide a display with private and public viewing modes. This has also been proposed for 3D autostereoscopic displays, for example in WO 2013/179190.
This document discloses a lens-based autostereoscopic display device, in which a light blocking arrangement is provided between adjacent lens locations and the display is configurable in at least two different modes: a privacy mode in which the light blocking arrangement blocks light which is directed between the lenses; and a public mode in which the light blocking arrangement does not block the light which is directed between the lenses.
The switchable privacy mode is able to turn on and off cone repetition. With cone repetition, the display functions exactly like a regular lens-based autostereoscopic display, with a wide viewing angle similar to a regular 3D lenticular display. Without cone repetition (because of the blocking function between lenses), only the primary cone is visible and all other cones appear black. In the privacy mode, the output brightness to the desired viewing cone is not reduced, and the full display resolution is used.
The 3D lenticular display may also be switchable between a 2D and 3D mode, either because the lens is electro-optically switchable or because the lens is birefringent and the polarization of the display panel can be controlled. Especially when the light modulation by the light blocking arrangement is not based on polarization, the two functions can be independent and there can be four combined modes (2D private, 2D public, 3D private and 3D public).
The light blocking structures are however potentially difficult to manufacture, as they are vertical structures.
US 2009/0067156 discloses a display system with a variable angular illumination range. A narrow emitting backlight is used for a narrow private mode and a wide emitting backlight is used for a wide public mode.
There is therefore a need for a light blocking arrangement for implementing public and private modes which can be implemented with low cost and low complexity.